A sheet size different than the above is calculated as a fraction or multiple of the basis weight and is normally noted for 1,000 sheets rather than 500. The weight thus calculated of the acutal sheet size is always noted in weight per thousand (M in roman numerals) and therefore said to be 19 X 25" - 100M meaning that 1,000 sheets of 19 x 25" will weigh 100 lbs.

Paper M-Weight Calculator | Case Paper

The weight (in pounds) of a (500 sheets) of paper cut to the for a particular of paper. The basic size of is 25 x 38. If 500 sheets weighs 70 pounds, then the basis weight is 70 pounds. Paper is commonly identified using basis weight: 20-pound , 80-pound , and so on. Size-and-weight tables, however, frequently give basis weight per thousand sheets. For example, a 25 x 38 70-pound book paper could be listed as "25 x 38—140M." The "M" signifies one thousand sheets, so to use the more conventional basis weight notation, the 140 should be halved, and it is then found that the basis weight (per 500 sheets) is 70 pounds. The basic size is not the same for all paper grades. Paperboards are commonly signified as pounds per 1,000 square feet. (See .)

The basis weight of a paper is determined by weighing a sample cut to the basic size for that grade on a "basis weight scale" that is designed to determine the weight of 500 sheets of the paper being measured. Basis weight strongly influences the strength properties of a paper, as well as such other properties as thickness, opacity, and runnability. (See .)

Basis weight is determined by weighing 500 sheets of paper.

A well beaten/refined pulp, short fiber pulp such as hard wood or straw pulp,highly filled or loaded paper will show lower thickness for given basis weight.